In recent years, accompanied by downsizing and enhanced performance of mobile devices, a nonaqueous electrolytic storage element has improved properties as a nonaqueous electrolyte storage element having high energy density and become widespread. Also, attempts are underway to improve gravimetric energy density of the nonaqueous electrolytic storage element, aiming to expand its application to electric vehicles.
Conventionally, a lithium ion nonaqueous electrolytic storage element including a positive electrode of a lithium-cobalt composite oxide, a negative electrode of carbon, and a nonaqueous electrolyte obtained by dissolving lithium salt in a nonaqueous solvent has been widely used as the nonaqueous electrolytic storage element.
Meanwhile, there is a nonaqueous electrolytic storage element, which is charged and discharged by intercalation or deintercalation of anions in a nonaqueous electrolyte to a positive electrode of a material, such as an electroconductive polymer, and a carbonaceous material, and by intercalation or deintercalation of lithium ions in the nonaqueous electrolyte to a negative electrode of a carbonaceous material (this type of battery may be referred to as “dual carbon battery cell” hereinafter) (see PTL 1).
In the dual carbon battery cell, as indicated by the following reaction formula, the cell is charged by intercalation of anions such as PF6− from the nonaqueous electrolyte to the positive electrode and by intercalation of Li+ from the nonaqueous electrolyte to the negative electrode, and the cell is discharged by deintercalation of anions such as PF6− and so on from the positive electrode and deintercalation of Li+ from the negative electrode to the nonaqueous electrolyte.

A discharge capacity of the dual carbon battery cell is determined by an anion storage capacity of the positive electrode, an amount of possible anion release of the positive electrode, a cation storage amount of the negative electrode, an amount of possible cation release of the negative electrode, and an amount of anions and amount of cations in the nonaqueous electrolyte. Accordingly, in order to improve the discharge capacity of the dual carbon battery cell, it is necessary to increase not only a positive electrode active material and a negative electrode active material, but also an amount of the nonaqueous electrolyte containing lithium salt (see NPL 1).
In the manner as described above, a nonaqueous electrolytic storage element, in which charging is performed by accumulating anions from a nonaqueous electrolyte to a positive electrode, and accumulating cations from the nonaqueous electrolyte to a negative electrode, and discharging is performed by releasing anions from the positive electrode and cations from the negative electrode, requires a sufficient amount of an electrolyte salt. It is important to provide a nonaqueous electrolyte in a limited volume of a nonaqueous electrolytic storage element in order to improve a volume energy density of a storage element. When a separator is designed to have a thick thickness to include a sufficient amount of a nonaqueous electrolyte, however, a problem that the energy density is reduced is caused.
In a nonaqueous electrolytic storage element using a lithium accumulating and/or releasing positive electrode, such as an oxide complex positive electrode, and a lithium accumulating and/or releasing negative electrode, such as graphite, a concentration of an electrolyte salt is not substantially changed with charging and discharging. Therefore, a density of an electrode is set high to pack a large amount of a storing material inside a storage element (to increase an energy density of the storing element), which lowers a porosity of the electrode. In a case where an storage element is composed to have the same structure to that of such storage element where a density of the electrolyte salt is not substantially changed with charging and discharging, an amount of a nonaqueous electrolyte that can be included inside the storage element is reduced, and there is a problem that a sufficient charging capacity and discharging capacity cannot be attained as a concentration of the electrolyte salt is reduced. When a thickness of a separator is increased to substantially increase an amount of a nonaqueous electrolyte to solve the aforementioned problem, an energy density of a nonaqueous electrolytic storage element is reduced by an increased amount of the separator, which does not contribute to storage of electricity.
Further, in a case where a concentration of an electrolyte salt is made high. i.e., about 3 mol/L, in a nonaqueous electrolytic storage element using a type of electrode where anions are stored in a positive electrode, and a case where the storage element is charged to high voltage, there is a problem that a capacity of the storage element is reduced.
Accordingly, it is desired to provide a nonaqueous electrolytic storage element, which realizes a high energy density and have an improved charging-discharging cycle properties.